1. Field of the Invention
The present invention relates to a scroll compressor, and more particularly, to a step-type capacity varying apparatus of a scroll compressor capable of performing an optimum driving in a corresponding condition by increasing a variation width of a compression capacity and capable of simplifying a capacity conversion.
2. Description of the Conventional Art
Generally, a compressor converts electric energy into kinetic energy, and compresses refrigerant gas by the kinetic energy. The compressor is an important component constituting a refrigerating cycle system, and includes a rotary compressor, a scroll compressor, a reciprocal compressor, etc. according to a compression mechanism. The refrigerating cycle system including the compressor is applied to a refrigerator, an air conditioner, a showcase, etc.
In a scroll compressor, a driving force of a driving motor is transmitted to an orbiting scroll and the orbiting scroll performs an orbiting motion in engagement with a fixed scroll, thereby sucking, compressing, and discharging gas. The orbiting scroll and the fixed scroll are respectively provided with a wrap of an involute shape, and a plurality of compression pockets are formed by the wrap of the fixed scroll and the wrap of the orbiting scroll. As the compression pockets move to a discharge hole for discharging gas as the orbiting scroll performs an orbiting motion, each volume of the compression pockets is gradually decreased thereby to compress gas.
Generally, a pair of compression pockets are formed to be symmetrical with each other on the basis of a discharge port. The two compression pockets have the same volume. When the pair of compression pockets move to a discharge hole after sucking gas at a suction side, another pair of compression pockets are formed at the suction side. The above process is repeatedly performed.
In order to increase a compression capacity compressed by the compression pockets, an asymmetrical scroll compressor in which one compression pocket has a larger volume than another compression pocket is being developed.
In the scroll compressor, under a state that an eccentric portion of a rotation shaft coupled to a driving motor is inserted into a boss portion provided at a lower portion of a disc of an orbiting scroll, a rotation force generated from the driving motor is transmitted to the boss portion of the orbiting scroll through the eccentric portion of the rotation shaft. However, when each volume of the compression pockets formed by the wrap of the fixed scroll and the wrap of the orbiting scroll is greatly varied, the orbiting scroll performs an unstable orbiting motion since the compression pockets for compressing gas are positioned with a certain distance from the boss portion and the eccentric portion to which a rotation force of the driving motor is transmitted.
As a structure for increasing a compression capacity of the scroll compressor, as shown in FIGS. 1 and 2, a wrap 12 having a certain height is formed at a disc 11 of the orbiting scroll 10. Also, a filling portion 13 having a certain height is formed at an inner end portion of the wrap 12 to be positioned at the center of the disc 11. The filling portion 13 is formed with a certain height so as to be positioned at the inner side of the wrap 12 from the inner end of the wrap 12 to a part corresponding to 360°. An insertion groove 14 for inserting an eccentric portion 21 of a rotation shaft 20 is formed at a lower surface of the disc 11 of the orbiting scroll, and the insertion groove 14 is formed up to the inner side of the filling portion 13. The eccentric portion 21 of the rotation shaft is inserted into the insertion groove 14. A section surface of the filling portion 13 is formed so that the eccentric portion 21 of the rotation shaft can be inserted thereinto.
Under the structure, since the eccentric portion 21 of the rotation shaft is positioned up to the inner side of the filling portion 13 of the orbiting scroll, the compression pocket P formed by the wrap 31 of the fixed scroll 30 and the wrap 12 of the orbiting scroll is overlapped with the eccentric portion 21 of the rotation shaft to which a rotation force is transmitted. According to this, the orbiting scroll 10 performs a stable orbiting motion in a condition of a large compression ratio. Also, since the filling portion 13 is formed at the center of the orbiting scroll wrap 12, a volume of a discharge side is largely decreased thereby to relatively increase a compression ratio of discharge gas. The above technique is disclosed in the JP 2000-329079.
In case of an air conditioner to which a refrigerating cycle system having a compressor is applied, it is necessary to vary a capacity of the compressor in order to reduce a consumption power of the air conditioner according to a season change.
A mechanism for varying a capacity of the compressor includes a method for controlling an RPM of a driving motor constituting the compressor, a method for bypassing or leaking gas, and a mixing method therebetween.
In the mechanism for controlling an RPM of a driving motor, a high fabrication cost is required even if a capacity variation width is wide and a function is excellent. Also, an additional device for supplying oil at a low RPM is necessary, and a reliability of a frictional part at a high RPM is required.
In the mechanism for bypassing gas, a capacity variation width is narrow and a function is low even if a fabrication cost can be lowered.